Array Operations in R Programming
Last Updated :
22 Apr, 2020
Arrays are the R data objects which store the data in more than two dimensions. Arrays are n-dimensional data structures. For example, if we create an array of dimensions (2, 3, 3) then it creates 3 rectangular matrices each with 2 rows and 3 columns. They are homogeneous data structures.
Now, let’s see how to create arrays in R. To create an array in R you need to use the function called array(). The arguments to this array() are the set of elements in vectors and you have to pass a vector containing the dimensions of the array.
Array_NAME <- array(data, dim = (row_Size, column_Size, matrices, dimnames)
where,
data – An input vector given to the array.
matrices – Consists of multi-dimensional matrices.
row_Size – Number of row elements that an array can store.
column_Size – Number of column elements that an array can store.
dimnames – Used to change the default names of rows and columns according to the user’s preference.
Example:
vector1 <- c(1, 2, 3)
vector2 <- c(10, 15, 3, 11, 16, 12)
result <- array(c(vector1, vector2), dim = c(3, 3, 2))
print(result)
|
Output:
, , 1
[,1] [,2] [,3]
[1,] 1 10 11
[2,] 2 15 16
[3,] 3 3 12
, , 2
[,1] [,2] [,3]
[1,] 1 10 11
[2,] 2 15 16
[3,] 3 3 12
Operations on Arrays
Naming columns and rows
We can give names to the rows and columns using dimnames.
Example:
vector1 <- c(1, 2, 3)
vector2 <- c(10, 15, 3, 11, 16, 12)
column.names <- c("COLUMN1", "COLUMN2", "COLUMN3")
row.names <- c("ROW1", "ROW2", "ROW3")
matrix.names <- c("Matrix.NO1", "Matrix.NO2")
result <- array(c(vector1, vector2), dim = c(3, 3, 2),
dimnames = list(row.names, column.names, matrix.names))
print(result)
|
Output:
, , Matrix.NO1
COLUMN1 COLUMN2 COLUMN3
ROW1 1 10 11
ROW2 2 15 16
ROW3 3 3 12
, , Matrix.NO2
COLUMN1 COLUMN2 COLUMN3
ROW1 1 10 11
ROW2 2 15 16
ROW3 3 3 12
Manipulating array elements
An array is made up of multiple dimensions and the operations are carried out by accessing elements.
Example:
vector1 <- c(1, 2, 3)
vector2 <- c(4, 6, 8, 0, 2, 4)
array1 <- array(c(vector1, vector2), dim = c(3, 3, 2))
vector3 <- c(3, 2, 1)
vector4 <- c(2, 4, 6, 8, 3, 5)
array2 <- array(c(vector3, vector4), dim = c(3, 3, 2))
matrix1 <- array1[,,2]
matrix2 <- array2[,,2]
result <- matrix1 + matrix2
print(result)
|
Output:
[,1] [,2] [,3]
[1,] 4 6 8
[2,] 4 10 5
[3,] 4 14 9
Accessing Array elements
Using index position in matrix any element can be accessed easily. Also, we can alter/change the element in an array using index position.
Syntax:
Array_Name[row_position, Column_Position, Matrix_Level]
Example:
vector1 <- c(1, 2, 3)
vector2 <- c(10, 15, 3, 11, 16, 12)
column.names <- c("COLUMN1", "COLUMN2", "COLUMN3")
row.names <- c("ROW1", "ROW2", "ROW3")
matrix.names <- c("Matrix.NO1", "Matrix.NO2")
result <- array(c(vector1, vector2), dim = c(3, 3, 2),
dimnames = list(row.names, column.names, matrix.names))
print(result)
print(result[3,,2])
|
Output:
, , Matrix.NO1
COLUMN1 COLUMN2 COLUMN3
ROW1 1 10 11
ROW2 2 15 16
ROW3 3 3 12
, , Matrix.NO2
COLUMN1 COLUMN2 COLUMN3
ROW1 1 10 11
ROW2 2 15 16
ROW3 3 3 12
COLUMN1 COLUMN2 COLUMN3
3 3 12
Calculation across array element
apply() function is used for calculations across array elements.
Syntax:
apply(x, margin, fun)
where,
x – an array.
margin – name of the dataset used.
fun – function to be applied to the elements of the array.
Example:
vector1 <- c(3, 2, 1)
vector2 <- c(2, 4, 6, 8, 0, 1)
new.array <- array(c(vector1, vector2), dim = c(3, 3, 2))
print(new.array)
result <- apply(new.array, c(1), sum)
print(result)
|
Output:
, , 1
[,1] [,2] [,3]
[1,] 3 2 8
[2,] 2 4 0
[3,] 1 6 1
, , 2
[,1] [,2] [,3]
[1,] 3 2 8
[2,] 2 4 0
[3,] 1 6 1
[1] 26 12 16
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